[PATCH v2 2/3] rust: crypto abstractions for random number generator API

[FUJITA Tomonori <fujita.tomonori@gmail.com>]

This patch adds basic abstractions for random number generator API,
wrapping crypto_rng structure.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
---
 rust/bindings/bindings_helper.h |   1 +
 rust/helpers.c                  |  12 ++++
 rust/kernel/crypto.rs           |   1 +
 rust/kernel/crypto/rng.rs       | 101 ++++++++++++++++++++++++++++++++
 4 files changed, 115 insertions(+)
 create mode 100644 rust/kernel/crypto/rng.rs

diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 2f198c6d5de5..089ac38c6461 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -7,6 +7,7 @@
  */
 
 #include <crypto/hash.h>
+#include <crypto/rng.h>
 #include <linux/errname.h>
 #include <linux/slab.h>
 #include <linux/refcount.h>
diff --git a/rust/helpers.c b/rust/helpers.c
index 7966902ed8eb..e4dcd611738f 100644
--- a/rust/helpers.c
+++ b/rust/helpers.c
@@ -19,6 +19,7 @@
  */
 
 #include <crypto/hash.h>
+#include <crypto/rng.h>
 #include <linux/bug.h>
 #include <linux/build_bug.h>
 #include <linux/err.h>
@@ -52,6 +53,17 @@ int rust_helper_crypto_shash_init(struct shash_desc *desc) {
 	return crypto_shash_init(desc);
 }
 EXPORT_SYMBOL_GPL(rust_helper_crypto_shash_init);
+
+void rust_helper_crypto_free_rng(struct crypto_rng *tfm) {
+	crypto_free_rng(tfm);
+}
+EXPORT_SYMBOL_GPL(rust_helper_crypto_free_rng);
+
+int rust_helper_crypto_rng_generate(struct crypto_rng *tfm, const u8 *src,
+	unsigned int slen, u8 *dst, unsigned int dlen) {
+	return crypto_rng_generate(tfm, src, slen, dst, dlen);
+}
+EXPORT_SYMBOL_GPL(rust_helper_crypto_rng_generate);
 #endif
 
 __noreturn void rust_helper_BUG(void)
diff --git a/rust/kernel/crypto.rs b/rust/kernel/crypto.rs
index f80dd7bd3381..a1995e6c85d4 100644
--- a/rust/kernel/crypto.rs
+++ b/rust/kernel/crypto.rs
@@ -3,3 +3,4 @@
 //! Cryptography.
 
 pub mod hash;
+pub mod rng;
diff --git a/rust/kernel/crypto/rng.rs b/rust/kernel/crypto/rng.rs
new file mode 100644
index 000000000000..683f5ee464ce
--- /dev/null
+++ b/rust/kernel/crypto/rng.rs
@@ -0,0 +1,101 @@
+// SPDX-License-Identifier: GPL-2.0
+
+//! Random number generator.
+//!
+//! C headers: [`include/crypto/rng.h`](../../../../include/crypto/rng.h)
+
+use crate::{
+    error::{code::EINVAL, from_err_ptr, to_result, Result},
+    str::CStr,
+};
+
+/// Type of Random number generator.
+///
+/// # Invariants
+///
+/// The pointer is valid.
+enum RngType {
+    /// Uses `crypto_default_rng`
+    // We don't need to keep an pointer for the default but simpler.
+    Default(*mut bindings::crypto_rng),
+
+    /// Allocated via `crypto_alloc_rng.
+    Allocated(*mut bindings::crypto_rng),
+}
+
+/// Corresponds to the kernel's `struct crypto_rng`.
+pub struct Rng(RngType);
+
+impl Drop for Rng {
+    fn drop(&mut self) {
+        match self.0 {
+            RngType::Default(_) => {
+                // SAFETY: it's safe because `crypto_get_default_rng()` was called during
+                // the initialization.
+                unsafe {
+                    bindings::crypto_put_default_rng();
+                }
+            }
+            RngType::Allocated(ptr) => {
+                // SAFETY: The type invariants of `RngType` guarantees that the pointer is valid.
+                unsafe { bindings::crypto_free_rng(ptr) };
+            }
+        }
+    }
+}
+
+impl Rng {
+    /// Creates a [`Rng`] instance.
+    pub fn new(name: &CStr, t: u32, mask: u32) -> Result<Self> {
+        // SAFETY: There are no safety requirements for this FFI call.
+        let ptr = unsafe { from_err_ptr(bindings::crypto_alloc_rng(name.as_char_ptr(), t, mask)) }?;
+        // INVARIANT: `ptr` is valid and non-null since `crypto_alloc_rng`
+        // returned a valid pointer which was null-checked.
+        Ok(Self(RngType::Allocated(ptr)))
+    }
+
+    /// Creates a [`Rng`] instance with a default algorithm.
+    pub fn new_with_default() -> Result<Self> {
+        // SAFETY: There are no safety requirements for this FFI call.
+        to_result(unsafe { bindings::crypto_get_default_rng() })?;
+        // INVARIANT: The C API guarantees that `crypto_default_rng` is valid until
+        // `crypto_put_default_rng` is called.
+        Ok(Self(RngType::Default(unsafe {
+            bindings::crypto_default_rng
+        })))
+    }
+
+    /// Get a random number.
+    pub fn generate(&mut self, src: &[u8], dst: &mut [u8]) -> Result {
+        if src.len() > u32::MAX as usize || dst.len() > u32::MAX as usize {
+            return Err(EINVAL);
+        }
+        let ptr = match self.0 {
+            RngType::Default(ptr) => ptr,
+            RngType::Allocated(ptr) => ptr,
+        };
+        // SAFETY: The type invariants of `RngType' guarantees that the pointer is valid.
+        to_result(unsafe {
+            bindings::crypto_rng_generate(
+                ptr,
+                src.as_ptr(),
+                src.len() as u32,
+                dst.as_mut_ptr(),
+                dst.len() as u32,
+            )
+        })
+    }
+
+    /// Re-initializes the [`Rng`] instance.
+    pub fn reset(&mut self, seed: &[u8]) -> Result {
+        if seed.len() > u32::MAX as usize {
+            return Err(EINVAL);
+        }
+        let ptr = match self.0 {
+            RngType::Default(ptr) => ptr,
+            RngType::Allocated(ptr) => ptr,
+        };
+        // SAFETY: The type invariants of `RngType' guarantees that the pointer is valid.
+        to_result(unsafe { bindings::crypto_rng_reset(ptr, seed.as_ptr(), seed.len() as u32) })
+    }
+}
-- 
2.34.1